A lighting source, such as a light-emitting diode (LED) light source, is typically driven by a load regulation device (e.g., such as an LED driver) in order to illuminate. A common control method for dimming an LED light source controlled by an LED driver is “zero-to-ten-volt” (0-10V) control, which is sometimes referred to as 1-10V control. A 0-10V LED driver receives power from an AC power source, with an external mechanical switch typically coupled between the AC power source and the 0-10V driver to provide a switched-hot voltage to the driver. Alternatively, the switched-hot voltage may be generated by an external power device (e.g., a power pack). The 0-10V driver controls the intensity of the connected LED light source in response to a 0-10V control signal received from a 0-10V control device (e.g., a 0-10V controller). Often, the 0-10V control device is mounted in an electrical wallbox and comprises an intensity adjustment actuator (e.g., a slider control). The 0-10 V control device regulates the direct-current (DC) voltage level of the 0-10V control signal provided to the driver between a substantially low voltage (e.g., zero to one volt) to a maximum voltage (e.g., approximately ten volts) in response to an actuation of the intensity adjustment actuator. For example, the 0-10V driver may control the intensity of the LED light source to a low-end intensity LLE (e.g., approximately 0.1%-10%) when the DC voltage level of the 0-10V control signal is at the substantially low voltage (e.g., zero to one volt) and to a high-end intensity LHE (e.g., approximately 100%) when the DC voltage level of the 0-10V control signal is at the maximum voltage (e.g., approximately ten volts).
To turn off the LED light source controlled by the 0-10V driver, power is removed from the 0-10V driver by, for example, controlling the switched-hot voltage to zero volts. The 0-10V control device may comprise a switching circuit for generating the switched-hot voltage. The switching circuit may include, for example, a mechanical air-gap switch, a relay, and/or a bidirectional semiconductor switch, such as a triac, one or more silicon-controlled rectifiers (SCRs), a field-effect transistor (FET) in a rectifier bridge, two FETs in anti-series connection, one or more insulated-gate bipolar junction transistors (IGBTs), or any suitable semiconductor switching circuit. In some cases, the 0-10V control device may be powered via the 0-10V control wires, for example, by drawing current from the 0-10V driver. Prior art 0-10V drivers typically source between 1-2 milliamperes of current, which the 0-10V control device may use to power itself.
Some 0-10 V drivers may be responsive to occupancy sensors, vacancy sensors, and/or daylight sensors. If the switched-hot voltage is controlled to zero volts to turn off the LED light source (e.g., by opening the switching circuit of the 0-10V control device or the power pack), the 0-10V driver will then be unpowered and unable to respond to the occupancy sensors, vacancy sensors, and/or daylight sensors.
Rather than removing power from an 0-10V driver to turn off the LED light source, the 0-10V driver may be controlled to an electronic off (e.g., standby) state in which the 0-10V driver remains powered, but turns off the LED light source. The 0-10V driver may be configured to change between an on state and the electronic off state in response to the 0-10V signal (e.g., using hysteresis). For example, during the on state, the 0-10V control device may be configured to adjust the DC voltage level of the 0-10V control signal between a minimum level (e.g., approximately 0.61-1.00 volts) and a maximum level (e.g., approximately ten volts) to adjust the intensity of the LED light source between the low-end intensity LLE and the high-end intensity LHE, respectively. To control the 0-10V driver into the electronic off state, the 0-10V control device may be configured to adjust the DC voltage level of the 0-10V control signal to a standby level. For example, the 0-10V driver may be configured to change to the electronic off state when the DC voltage level of the 0-10V control signal drops below a falling threshold (e.g., approximately 0.6 V). The 0-10V driver may be configured to return to the on state (e.g., to turn on) when the DC voltage level of the 0-10V control signal rises above a rising threshold (e.g., approximately 1.0 V), after which the 0-10V driver may adjust the intensity of the LED light source between the low-end intensity LLE and the high-end intensity LHE as the 0-10V control signal ranges between the minimum level and the maximum level.
Since the falling threshold may be approximately 0.6 V, the DC voltage level of 0-10V control signal may be as low as 0.61 V when the 0-10V driver is being controlled to the low-end intensity LLE. This means that the DC voltage level of 0-10V control signal at the low-end intensity LLE may be between the rising threshold and the falling threshold. If there is a momentary interruption of the power, such as a power outage or a manual switch-off of power to the 0-10V driver when the 0-10V driver is in the on state, and the DC voltage level of the 0-10V control signal is between the rising threshold and the falling threshold, the 0-10V driver may not turn back on when power is restored (e.g., re-applied) because the DC voltage level of 0-10V control signal will not be above the rising threshold. It is undesirable for a lighting load that is on to not turn back after a momentary power interruption.